The mystery of the disappearing chicken

A few weeks ago we bought some ex battery hens. For those of you who don't know, battery hens spend their whole lives in cages and can't do any of the things that chickens like to do. They are basically egg laying machines. At quite a young age ( I'm not sure exactly what age but inbetween two and three years I think) they are slaughtered as their peak production years are deemed to be over. I assume they are then used as dog and cat food. A chicken can live to be ten or more.
In our area, every now and then an ex battery hen sale is held. The hens are sold very cheaply and avoid slaughter. As our light sussex hens were only producing eggs very sporadically we decided to buy a few ex battery hens. At first we kept them in an ark so they could go in and out as they pleased but not stray. At first they were too frightened to go outside but eventually did. Chickens are naturally inquisitive creatures and will peck at anything. They began to peck at the grass and discovered how tasty it was. Our other chickens spent quite a lot of time 'talking' to them through the netting and after about ten days the big occasion of letting them roam free came.
Malcolm, our cockerel took charge of them straight away and showed them around. After a couple of days I was lucky enough to see him teach them how to  bathe. Chickens love to dust bathe. They make an indentation in a dry piece of ground and roll around in it, even stretching out their wings to do underneath. They then spend a long time preening. This helps to get rid of parasites and is obviously very pleasurable. The next day Malcolm bought them to the back door knowing that I would give them some bread or seeds as a treat. They have become very confident over the last few weeks and mob me for treats as soon as I walk out of the door. In fact, if I leave the door open for a short while they are in! I spend quite a lot of time chasing them out of the kitchen.
Usually, when it starts to get dark they all go to their house and wait to be fed before settling down for the night. It is very important to lock them in at dusk as there are lots of foxes in our area who are quick to grab any stray chickens for their dinner.
One day last week I went to feed them and put them to bed as usual and one was missing. I checked in their house but she was not there. After feeding the other animals I went round checking the polytunnels in case she had managed to squeeze in and not get out. I checked the feed store and the outbuilding where we store logs. The chickens often like to hang out there in bad weather.  I checked under hedges and every where else I could think of but there was no sign of her. Not even a few feathers to show that the fox had come early and carried her off.
The next day I still could not find her. The others were all wandering around as usual but she was not there. I assumed that she had been eaten by something and felt quite sad.That night I fed the chickens and ducks then went in to the field to feed the sheep and pigs. Just as I was shutting the gate, along sauntered the missing chicken. I opened the gate and she came out of the field and casually walked over to her house, looking at me to let her in.

I still have no idea where she went or how she survived a night outside but am pleased that she is back and safe.